1. Field of the Invention
The present invention relates to an organic electroluminescent device that emits light by converting an electric energy into light.
2. Background Art
Research and development are being vigorously made on organic electroluminescent devices (which may hereinafter be called “organic EL devices”) because they can emit light with a high luminance even by low voltage driving. Organic electroluminescent devices each has one or more organic layers between a pair of electrodes. For light emission, they utilize energy of an exciton generated as a result of recombination, in the organic layers, of electrons injected from a cathode and holes injected from an anode.
In recent years, phosphorescent materials have been used to promote the efficiency of the device. There is disclosed an invention related to an organic electroluminescent device having improved long-term storage stability and less dark spots by using a compound having an N-phenylcarbazole skeleton between an organic light emitting layer and a cathode for improving the adhesion with the cathode (refer to Japanese Patent Laid-Open Nos. 8-88083 and 8-60144).
WO 04/101707 discloses an invention related to an organic electroluminescent device using, as a host material for forming a light emitting layer in cooperation with an iridium complex material, a compound having, for example, an N-phenylcarbazole skeleton represented by the following formula:

The device using the above compound has however insufficient durability and in addition, needs a further improvement in drive voltage.
Japanese Patent Laid-Open No. 2003-335753 discloses an invention related to an organic electroluminescent device using, for the light emitting layer thereof, for example an N-phenylcarbazole compound represented by the following formula:

The device using the compound has however insufficient durability and in addition, needs a further improvement in drive voltage.